1. Field of the Invention
The invention is in the field of battery technology.
2. Related Art
Four basic design parameters of a battery/fuel cell (battery) include energy density, power density, cycle life, and safety. Energy density refers to how much energy the battery can store, measured in units of mega-joules/kilogram (MJ/kg.) Power density (also referred to as power-to-weight ratio and specific power) refers to how quickly the stored energy per unit mass can be delivered, and is measured in units of kilowatts/kilogram (W/kg). Cycle life refers to the charge capacity of the battery vs. the number of charge/discharge cycles. Typically, a larger cycle life is more useful. Safety considerations for a battery include processes that could harm person or property, for example, toxic chemical release and overheating to the point of fire.
FIG. 1 illustrates a cross section of a prior art lithium-ion secondary (rechargeable) battery/cell 100. The secondary battery/cell 100 includes an anode 120, an electrolyte 140, a separator 130, an electrolyte 140, and a cathode 110. In some cases, the anode 120 includes graphite. Reasons for using graphite for the anode 120 include relative ease of Li-ion intercalation and low cost of graphite. Alternatively, the anode 120 includes silicon applied directly to the bulk (macroscopic) substrate of the anode. A reason for using silicon is that silicon can intercalate roughly ten times more Li-ions than graphite. Unfortunately, silicon typically expands 400% or more upon full Li-ion intercalation, which can cause silicon breakage and substantially compromise adhesion of silicon to the anode 120, thus, decreasing longevity.
The separator 130 between the secondary battery/cell 100 includes a porous membrane. In some embodiments, the porous membrane is a microporous polyolefin membrane. Microporous polyolefin does not participate in the reactions inside the battery. The separator 130 is typically about 50 microns thick and includes pores 135. A typical average of the size of the pores 135 is about of 2.0 microns or more.
The cathode 110 of the secondary battery/cell 100 is generally of three types. These three types include a layered oxide (such as LiCoO2, LiMnO2, or LiNiO2), a polyanion (such as lithium iron phosphate), or a spinel (such as manganese oxide). The material used for the cathode 110 is typically a bulk material or a bulk deposited/grown film. Unfortunately, due to the macroscopic nature of these materials, ion diffusion in the bulk material of the cathode 110 limits the oxidation and reduction rates during the charge and discharge cycles. The poor diffusion rates of the ions limits the overall power density. The cathode may be electrically coupled to an electrical contact point 150A for drawing current from the battery/cell 100. The anode may be electrically coupled to an electrical contact point 150B for drawing current from the battery/cell 100.
The electrolyte 140 in the secondary battery/cell 100 may be a salt dissolved in a solvent, such as LiClO4, LiPF6, LiBF4, and/or the like.